The present invention relates to liquid dispensing apparatus and pertains particularly to an improved infuser apparatus for delivering intravenous drugs at a controlled rate to a patient.
It is often necessary to intravenously supply patients with pharmaceutically active liquids over a long period of time at a controlled rate. It is desirable that this be accomplished while the patient is in an ambulatory state. A few devices have been developed in the past for accomplishing this purpose.
The prior art devices typically comprise an elastic bladder forming a liquid container mounted in an elongated cylindrical housing, and having a flow control valve or device and tubing for supply of the liquid to the patient. The elastic walls of the bladder expand along the walls of the cylindrical housing when filled with the liquid, and provide the pressure for expelling the liquid. These prior art devices are typically filled by hand by means of a syringe which often require an inordinate amount of force.
Another drawback to the prior art devices is that the bladder is forced to expand into an unnatural elongated configuration along the housing walls as the container is filled. As a result of this unnatural configuration, the pressure of the bladder and the flow rate of the unit varies widely with the volume of liquid therein. Therefore, they do not have a reasonably stable pressure and flow rate over the infusion period.
Most of such devices either have a flow rate that decreases with pressure, which decreases with volume, or one that remains roughly constant until the end where it surges. Attempts have been made to control pressure and flow rates by means of complicated and expensive flow control valves and devices. Other approaches have utilized exotic and expensive elastic materials in an effort to control the pressures and flow rates.
In our aforementioned application, we disclose an apparatus for solving the aforementioned problems of the prior art. However, one problem remains, namely that the materials that provide optimum elasticity do not have sufficient chemical inertness for medical application. Similarly, materials that are sufficiently chemically inert for medical or pharmaceutical use are not sufficiently elastic to serve the function of an effective inflatable bladder.
It is desirable that the bladder of an inflatable bladder infuser be chemically inert in order to avoid contamination of the medication, and that the pressure and flow rate be reasonably constant over the infusion period.
Accordingly, it is desirable that an improved infuser apparatus be available.